1. Field of the Invention
This invention relates to a means for generating an implosive sound and more specifically to an implosive sound projector that is controllable and emits a highly localized, spatially and temporally oriented acoustic wave for underwater communication, detection, and classification of submerged objects.
2. Description of the Related Art
Current technology for generating an impulsive sound waves in an aquatic medium is based on a detonation mechanism, such as imploding glass spheres, an explosive charge, or electric spark. An acoustic signal obtained by these methods is difficult to control because of the variation in input energy between explosive sources or spark gap deterioration when using an electric spark source, as well as the interference caused by bubble resonances. A broad band acoustic source can also be achieved with a frequency synthesizer, however the final signal is not localized in the time domain and the energy conversion efficiency is very poor due to the required compensation for the frequency response during electro-mechanical transduction. See, U.S. Pat. No. 4,805,726, Taylor et al., issued Feb. 21, 1989; U.S. Pat. No. 4,185,714, Pascouet et al., issued Jan. 29, 1980.
When a cavity suddenly implodes, or collapses, under hydrostatic pressure, an impulse sound is produced that can be measured by a remote listening device. Such an implosion sound has similar characteristics to that sound produced by an explosive but is much safer. Implosive sound is highly localized in time and space which is very useful for applications in areas that require high temporal resolution, for example, in undersea oil exploration. The selection of the size of the implosion sound projector depends on its particular application. Although fundamental relations described in this invention do not include the effect of scaling factor on the performance of implosion sound generation, the heat conduction and interface stability between the fluid and gas become important as its physical size increases.